Root mean square sensor device

ABSTRACT

A sensor device includes a first and second Micro-Electro-Mechanical (MEM) structures. The first MEM structure includes a first heating element on a first layer of the first MEM structure. The first heating element includes an input adapted to receive an input signal. The first MEM structure also includes a first temperature sensing element on a second layer of the first MEM structure. The second MEM structure includes a second heating element on a first layer of the second MEM structure and a second temperature sensing element on a second layer of the second MEM structure. An output circuit has a first input coupled to the first temperature sensing element and a second input coupled to the second temperature sensing element.

TECHNICAL FIELD

This disclosure relates to a root mean square sensor device.

BACKGROUND

The root mean square (RMS) value of an alternating current (AC) is alsoknown as its heating value, as it is a voltage which is equivalent tothe direct current (DC) value that would be required to get the sameheating effect. A thermal converter is a device that includes a heatingelement and temperature sensing element configured to convert an ACinput signal into a corresponding RMS value. For example, an AC signalis applied to a heating element that is matched with a thermistor (orother temperature sensing element) that is used in a DC measuringcircuit to provide an output representative of the DC value.

SUMMARY

One example includes a sensor device that includes a firstMicro-Electro-Mechanical (MEM) structure and a second MEM structure. Thefirst MEM structure includes a first heating element on a first layer ofthe first MEM structure. The first heating element includes an inputadapted to receive an input signal. The first MEM structure alsoincludes a first temperature sensing element on a second layer of thefirst MEM structure, the first layer being separated from the secondlayer by at least one insulating layer. The second MEM structureincludes a second heating element on a first layer of the second MEMstructure and a second temperature sensing element on a second layer ofthe second MEM structure. The first layer of the second MEM structurebeing separated from the second layer of the second MEM structure by atleast one insulating layer. An output circuit has a first input coupledto the first temperature sensing element and a second input coupled tothe second temperature sensing element.

Another example includes a sensor circuit package that includes at leasttwo Micro-Electro-Mechanical (MEM) structures. Each of the MEMstructures includes a central core region including a thermal convertercircuit that is configured to heat the core region in response to asignal at an input thereof and to provide a temperature signalrepresenting a temperature of the heated central core region. A supportstructure is coupled between the central core region and surroundingsubstrate. The support structure is configured to support the centralcore region to be thermally and mechanically isolated with respect tothe surrounding substrate. An amplifier circuit is configured to providean amplifier signal at an output of the amplifier based on the outputsignals provided by the thermal converters of the respective MEMstructures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram depicting an example of a sensor device.

FIG. 2 depicts example of MEM structures that can be used to implement asensor device.

FIG. 3 depicts an example arrangement of MEM structures that may be usedto implement a sensor device.

FIG. 4 depicts another example arrangement of MEM structures that can beused to implement a sensor device.

FIG. 5 depicts an example of a MEM structure that includes a resistorand associated interconnects.

FIG. 6 is a cross-sectional view of a MEM structure taken along the line6-6 of FIG. 5.

FIG. 7 depicts an example of a sensor device that includes MEM thermalconverters coupled in a closed loop circuit topology.

FIG. 8 depicts another example of a sensor device that includes MEMthermal converters in a closed loop circuit topology and outputcircuitry implemented on a MEM structure.

FIG. 9 depicts an example of a sensor device that includes MEM thermalconverters in an open loop circuit topology.

FIG. 10 depicts an example of an integrated sensor package.

FIG. 11 depicts an example of a sensor device implementing the RMSconverter.

FIG. 12 depicts an example of a low-side current sensor circuit.

FIG. 13 depicts an example of a high-side current sensor circuit.

FIG. 14 depicts an example of another current sensor circuit.

FIG. 15 depicts an example of a DC-DC converter that includes a sensorcircuit to provide feedback.

FIG. 16 depicts an example of an isolated operational amplifier.

FIG. 17 depicts an example of a circuit to implement load balancing.

DETAILED DESCRIPTION

The disclosure relates a sensor device and system that includes a trueroot mean square (RMS) thermal converter configured to generate an RMSrepresentation based on one or more input signals. The RMS thermalconverter can be fully integrated in a low-cost injection molded plasticpackage to provide a high performance sensor device. Numerous sensor andcircuit topologies exist that can be utilized in various configurations.The sensor device offers high linearity and precision and can alsoprovide full galvanic isolation between input and output. In someexamples, the sensor device can be packaged in a low-cost injectionmolded plastic package. The sensor device thus may to maintain thermalisolation and exhibit performance that is independent of mechanicalstress induced in the silicon via the plastic package and printedcircuited board (PCB) on which the package is mounted. The sensor devicealso can reduce stress induced from environmental conditions (e.g.,humidity variations). This performance is achieved through use of amicrofabrication process that embeds a hermetic,micro-electro-mechanical (MEM) thermal converter structure that isisolated from the plastic package in which it is encapsulated.

As an example, a sensor device includes at least two MEM structures,each having a core region that includes a thermal converter circuitconfigured to provide an output signal that is an RMS value of an inputsignal received at an input. The MEM structures may be fabricated on acommon substrate (e.g., monolithic silicon), which enables the MEMstructures to be constructed as matching structures. The thermalconverter circuit of a MEM structure includes a heating element on afirst layer and a temperature sensing element on a second layer that isspaced apart from the first layer by at least one insulating layer(e.g., an oxide or other dielectric layer) that provides galvanicisolation between the input and the output of the thermal converter. Forexample, the heating element is a resistive element that is coupled toone or more inputs through respective interconnects. An input thus canbe adapted to receive an input signal from associated circuitry, such asmay be integrated on a PCB or otherwise connected to the input. Thetemperature sensing element (e.g., a diode, thermistor, bipolartransistor, MOSFET or thermocouple) is configured to provide atemperature signal representing the temperature of the heated coreregion in response to application of signal to the heating element. Forexample, the temperature signal from the heating element represents atrue RMS value of the input signal.

As a further example, the sensor device includes at least two such MEMstructures that are fabricated on a substrate (e.g., bulk silicone) asmatched structures (e.g., fabricated on a common substrate according toa common fabrication process). An output circuit is coupled to thetemperature sensing element of each MEM structure of the sensing device.For example, the output circuit includes an amplifier having inputscoupled to receive the temperature signals from the respectivetemperature sensing elements. In one example, the amplifier has anoutput coupled to a heating element of one of the MEM structures and isconfigured to drive such heating element in a closed loop manner tomatch the heating of the first heating element based on the temperaturesignals produced by the respective temperature sensing elements of eachMEM structure. In such closed loop circuit topology, the transferfunction linearity of the sensor can be increased relative to existingthermal converters.

In another example, the sensor device may be configured in an open loopcircuit topology. For example, the input of a first heating element isadapted to receive a first input signal. A second heating element ofanother MEM structure has another input that is adapted to receive asecond input signal. The inputs of the amplifier are coupled to receivetemperature signals from temperature sensing elements of each of the MEMstructures. The amplifier is thus configured to provide an output signalrepresenting a difference between the RMS values of the first and secondinput signals that are applied to the respective heating elements of theMEM structures.

As disclosed herein, each thermal converter is configured thus toprovide an output signal equivalent to the “heating value” or RMS valueof the applied input signal, regardless of that signals waveform.Advantageously, the MEM structure includes galvanic isolation betweeninput and output and further can operate from DC to high frequencies,such as GHz or higher. The MEM structure further affords isolation frommechanical stress due to packaging and thermal isolation. Moreover, dueto the small size of the heating element on the MEM structure, the inputimpedance of the converter can be such that it does not significant loadthe signal being measured.

FIG. 1 depicts an example of a sensor device 100. The sensor device 100includes two or more MEM structures 102 and 104. There can be any numberof each of the respective MEM structures 102 and 104 in a variety ofconfigurations as indicated by the ellipsis between the respectivestructures illustrated in FIG. 1. In one example, the MEM structures 102and 104 are implemented on the common base layer of the substratematerial (e.g., bulk silicon substrate) in a single die. In anotherexample, each of the MEM structures may be implemented in separate diethat may be integrated into a common sensor package (e.g., a multi-chipsensor package).

Each of the MEM structures 102 and 104 may be produced by the samefabrication process and under the same process parameters. For example,the MEM structures 102 and 104 can be fabricated at the same time orsequentially according to a microfabrication process. Thus, the MEMstructures 102 and 104 are matched to be substantially identical (orproportional) devices and thus operate in a substantially identicalmanner. As used herein, the term substantially in this context is todenote that the construction and/or operation of the MEM structures 102and 104 are intended to be identical, but may differ slightly from theintended relationship within variations due to the fabrication processand the materials that are used. In the following examples, unlessindicated otherwise, the MEM structures are considered to besubstantially identical.

Each of the MEM structures 102 and 104 includes a thermal converterconfigured to implement a true RMS converter. For example, the MEMstructure 102 includes as heating element 106 that is implemented on alayer of the MEM structure that is separated from a temperature sensingelement 108 that is implemented on another layer. One or more insulating(dielectric) layers 110 separate the heating element 106 from thetemperature sensing element 108. For example, the insulating layer is anoxide layer is formed of an inter-metal dielectric that providesgalvanic isolation between the heating element 106 and the temperaturesensing element 108.

The heating element 106 is coupled to a terminal 114 of the device thatis adapted to receive an input signal 116 from another circuit or device(not shown). As an example, in response to the input signal 116 that isapplied to the terminal 114, electrical current flows through theheating element to heat a region of the MEM structure 102. Thetemperature sensing element 108 is arranged in the region and thussenses the rise in temperature and provides a corresponding outputsignal representative of such heating. The output signal (in response tothe heating) represents an RMS value of the input signal at 114. Thetemperature sensing element 108 provides the output signal at an output118 thereof that is coupled to an input of an output circuit 130.

As mentioned, the other MEM structure 104 is configured the same as MEMstructure 102 and thus includes a heating element 120, a temperaturesensing element 122 and one or more insulating layers 124. The heatingelement 120 is coupled to a terminal 126 of the sensor device and atemperature sensing element has an output 128 that is coupled to anotherinput of the output circuit 130. As with MEM structure 102, the MEMstructure 104 is configured as a thermal converter, such that a heatingelement 120 heats a region of the MEM structure 104 and such heating isdetected by the temperature sensing element 122. The temperature sensingelement 122 thus provides an output signal at 128 based on the heatingand thus representative of an RMS value of the signal provided at theterminal 126.

The output circuit 130 is coupled to receive the output signals providedat 118 and 128 from the temperature sensing elements 108 and 122 atrespective inputs. The output circuit 130 is configured to generate anoutput signal at 132 based on the temperature signals at 118 and 128. Asdisclosed herein, the output 132 of the output circuit 130 can beutilized for a variety of different purposes according to sensingrequirements and application specifics in which the sensor device 100 isused.

In one example, the output 132 can be coupled to the terminal 126 todrive the heating element 120 with feedback based on the signalsprovided at 118 and 128. In this closed loop example, the output circuit130 is configured to drive the heating element 120 until the temperatureof the heated regions in each of the MEM structures 102 and 104 areequal. In this example, the output signal at 132 represents the RMSvalue of the input signal 116 that is applied to the input terminal 114.In another example, another input signal may be applied to the terminal126. In this open loop example, the output circuit 130 provides theoutput 132 to represent a difference between the RMS values of thesignals applied at terminals 114 and 126.

As disclosed herein, the heated regions of the MEM structures 102 and104, which contain heating element, insulating layer(s) and temperaturesensing element, can correspond to a central core that is mechanicallyand thermally isolated from surrounding substrate material of the die inwhich the MEM structures 102 and 104 reside. For example, the coreregion can be surrounded by a vacuum or a volume of inert gas to reducethermal loss from the core region. Additionally, each of the MEMstructures may include a support structure, such as an arrangement ofsupport arms, connected between the surrounding substrate and therespective core regions such that the core regions are floating withinthe semiconductor die. The support structure (mechanically) isolates thecentral core region from packing stress that may be applied to thesurrounding substrate. Additionally, to enhance thermal isolation of thecore region, the core region (on which the thermal converter circuitryresides) can be sandwiched between a cap and base layer of the die. Forexample, the cap and base layer thus may be applied to enclose andhermetically seal each core region within the die surrounded by a vacuumor region of inert gas. In the example MEM structure implementing thefloating core region, a dominant conductive thermal loss path is throughthe support arms. This thermal loss can be managed by design of thesupport arm structure. For example, the thermal loss can be controlledby setting the length and cross-sectional area of each arm as well asarranging the arms symmetrically along a perimeter of the core region.

FIG. 2 depicts an example of a sensor device 200 that includes a pair ofMEM structures 202 and 204 (e.g., corresponding to MEM structures 102and 104). The sensor device 200 is fabricated on a substrate material206, such as a bulk silicon substrate. Each MEM structure 202 and 204includes a respective central core region 208 and 210 that is supportedto be floating with respect to the surrounding substrate 206. Asdisclosed herein, the central core regions 208 and 210 are thermally andmechanically isolated from the surrounding substrate by a vacuum regionor hollow region containing an inert gas. For example, a gap between theouter surfaces of each central core region 208, 210 and adjacentsubstrate may be formed by etching or otherwise cutting away respectivelayers of the die structure leaving only a supporting structure tosupport the central core region in the device 200.

By way of example, the MEM structure 202 includes an arrangement ofsupport arms 212 configured to hold the floating central core withrespect to the surrounding substrate 206. For example, each support arm212 is a generally T-shaped structure that includes a base portion 214,a central arm portion 216 and a support portion 218. The base portion isconnected to and extends from the surrounding substrate 206. The centralarm portion 216 extends orthogonally from the base portion and parallelto an adjacent perimeter portion of the central core 208. The supportportion 218 extends from an opposite end of the arm portion 216 and isconnected near a corner of the central core 208. In one example, foursupport arms 212 are arranged symmetrically along respective side edgesof central core 208 and are connected at respective corners to supportthe central core with respect to the surrounding substrate 206. Othernumbers and configurations of support structures may be used in otherexamples.

The support arms 212 may be formed of the same material as one of thelayers of the core, such as may be grown or deposited over a top layerthereof and etched or otherwise cut to form the arm structures. In anexample, the silicon substrate (e.g., wafer) may be patterned by aphotoresist. The photoresist protects the core, surrounding silicon andarms from etching allowing L-shaped voids 219 to form around and therebycreate the supporting arms 212. In this way, the support arms 212 areconfigured to support the central core region 208 with respect to thesurrounding substrate 206 to provide thermal and mechanical isolation ofthe core region relative to the substrate. The other MEM structure 204may be a replica of the MEM structure 202 and be formed concurrentlywith the MEM structure (e.g., through a process that includes applyingphotoresist and etching to form voids in the substrate 206 to definerespective arms 220). Briefly stated, the central core region 210 issupported with respect to the surrounding substrate 206 by anarrangement of support arms 220. For example, each support arm 220includes a base portion 222 connected to a surface of the substrate 206,an elongated arm portion 224 that extends from the base portion and asupport portion 226 that extends from the arm portion and is connectedto a corner of the central core 210.

As disclosed herein, each central region 208 and 210 includes a thermalconverter circuit configured to provide an output signal representing anRMS value of an input signal based on heating of the respective centralcore region. For example, FIG. 2 schematically illustrates the thermalconverter circuit of MEM structure 202 as including a heating element,demonstrated as a resistor 230, and a temperature sensing element,demonstrated as a diode 232. Likewise the thermal converter circuit ofthe MEM structure 204 includes a heating element, demonstrated as aresistor 234, and a temperature sensing element, demonstrated as a diode236. In each MEM structure 202 and 204, the respective resistor anddiode can be formed on separate layers of the central core region 210such as disclosed herein. While the temperature sensing devices aredemonstrated as a diode in FIG. 2, in other examples, the temperaturesensing devices may be implemented by other temperature dependentdevices, such as thermistors, bipolar transistors, MOSFETs orthermocouples.

Because the thermal converter circuit implemented on the central coreregion 210 is thermally and mechanically isolated from the surroundingsubstrate, the sensitivity of the thermal converter can be highercompared to existing thermal converters. Moreover, by including a pairof thermal converter circuits (or more), the sensor device 200 can beconstructed and used in a variety of sensing applications such asdisclosed herein (see e.g., FIGS. 7-16).

While the example of FIG. 2 demonstrates two MEM structures 202 and 204implemented for the sensor device 200, different numbers of MEMstructures can be implemented in other examples, such as demonstrated inFIGS. 3 and 4. In each of these examples, the respective MEM structuresdenoted as “A” correspond to an instance of a first MEM structure andrespective core regions denoted as “B” correspond to another MEMstructure. Each “A” structure is identical and each “B” structure isalso identical. In an example, each “A” structure is identical to each“B” structure. In another example, each “A” structure is matched to beproportional (e.g., having a desired ratio) with respect to each “B”structure. The arrangements of “A” and “B” structures, such asdemonstrated in FIGS. 3 and 4, facilitates fabrication a device in whichthe combination of all A devices parametrically match the combination ofall B devices. This also helps to improve linearity and reduced effectsfrom externally induced thermal gradients.

In the example of FIG. 3, a sensor device 300 includes MEM structures302, 304, 306 and 308 arranged as in a linear array of A-B-B-A on asemiconductor substrate. In this arrangement each “B” structure residesadjacent a respective “A” structure on the given semiconductorsubstrate. In the example of FIG. 4, a sensor device 400 includes MEMstructures 402, 404, 406 and 408 arranged as in a two-dimensional arrayof cross-coupled structures on a semiconductor substrate. As shown inFIGS. 3 and 4, the different “A” and “B” structures may be placed acrossthe die according to application requirements and best practices toachieve desired matching of identical or proportional devices. Byutilizing multiple pairs of “A” and “B” structures, various otherconfigurations and layouts may be implemented that exhibit improvedlinearity and reduced effects from externally induced thermal gradients.

FIGS. 5 and 6 depict an example of a MEM structure 500 to which aheating element 502 has been applied. The MEM structure 500 of FIGS. 5and 6 can be similar to the MEM structures shown and described withrespect to FIGS. 1, 2 and 4. Thus, the heating element of FIG. 5 may beutilized for heating the central core region in each of those examples.FIGS. 5 and 6 use common reference characters to refer to commonfeatures in both figures.

In the examples of FIGS. 5 and 6, the heating element 502 includesresistive element disposed on an oxide or other insulating layer of theMEM structure 500. For example, the heating element 502 is a spiral thinfilm resistor across the surface of an insulating layer 608 (e.g., anoxide layer) of the central core region 506. The thin film resistor maybe deposited (e.g., by sputtering) a layer of the electricallyconductive material over the insulating layer 608 and then etching aportion of the layer to provide a desired shape (e.g., spiral) resistoracross the surface of the central core region 506 spaced inwardly fromthe support arms 508 (e.g., corresponding to support arms 212) andassociated voids. As a further example, the resistive heating element502 is formed of a metal, such as nickel chromium (NiCr), siliconchromium (SiCr), aluminum or an alloy thereof. Other techniques andmaterials may be used to form the heating element on the insulatinglayer. The exposed surface of the resistive heating element may becoated with an insulating material or remain exposed to the vacuum orinert gas in the cavity that surrounds the central core region. In theexample of FIG. 5, the temperature sensing element 512 is schematicallyillustrated as a diode.

The heating element 502 is configured to heat a region of the bulksilicon in the central core region 506 below the heating element inresponse to a signal applied to the heating element. For example, theends of the resistive heating element 502 may be connected to terminals(not shown, but see, e.g., terminals 114, 126 as well as others) throughcorresponding interconnects 510 of electrically conductive material(e.g., a metal). The interconnects 510 can be coupled to the ends of theheating element 502, such as forming them between the support arms 508and over the passivation layer (layer 612 of FIG. 6) through respectivevias to couple with the heating element.

As demonstrated in the example FIG. 5, the heating element 502 may beimplemented as one or more windings of a rectangular spiral shape thatare distributed fairly evenly across the layer to which it is applied.In this way, a larger area of the bulk silicon (between the heatingelement 502 and temperature sensing element 512) may be heated inresponse to a signal applied to the resistant heating element 502disposed thereon. Additionally, the resistive heating element 502 may benon-inductive to minimize frequency dependencies of the heating element,such that the sensor device of the MEM structure 500 can operate overbroadband of input signals (e.g., from a DC to GHz or higher). Theheating element 502 may be made non-inductive by patterning it in such away the flux from one trace of the resistor cancels the flux from anadjacent trace. For example, by implementing the heating element 502 asan integrated resistor with pairs of conductive traces having opposingcurrents wrapped in a spiral, the flux can be cancelled and thus makethe inductance very low (e.g., negligible).

Referring to FIG. 6, the heating of the central core region 506 of theMEM structure 500 is isolated with respect to the surrounding substratebecause the central core region where the heating element 502 andtemperature sensing element 512 reside is surrounded by a cavity 614that includes a vacuum or an inert gas. For example, the cavity 614includes void formed by etching. The cavity 614 also is formed by astandoff spacing between the cap 620 and the floating core structure aswell as standoff distance between the bulk silicon base 604 and thefloating core structure. As a result, the thermal loss above and belowthe heating element 502 is mostly radiation loss and is minimal due tothe insulation of the surrounding vacuum or inert gas. For example, adominant conductive path for loss of thermal energy is through thesupport arms 508 because the support arms support the central coreregion of the MEM structure 500 where the heating element 502 resides.By configuring the support arms 508 to extend along the perimeter of thecentral core region 506, such as shown in FIG. 5, the loss through thearms 508 along the perimeter portion is symmetrical. Thus, thedimensions of the arms 508 can be a design parameter that can becontrolled, such as by setting the length and cross-sectional thicknessof each of the respective arms. In addition to being used to control thethermal loss of the heating region, the support arms 508 also areconfigured to isolate the central core region from packaging stress thatnormally effects circuitry and structures within packaging materials.

As shown in FIG. 6, which is a cross-sectional view 600 of the MEMstructure 500 of FIG. 5 taken along the lines 6-6, the resistive element502 is built on top of (or within) one or more insulating layers ofinter-metal dielectric. For example, the MEM structure 500 is formed ona silicon substrate (e.g., a wafer) that is joined to a bulk siliconbase 604. In other examples, other bulk semiconductor materials may beutilized as a corresponding substrate for constructing the MEMstructures disclosed herein. The central core region 506 is formed overthe silicon base substrate 602. For example, the central core region 506is spaced apart and insulated from the base layer 604 by the void thatsurrounds the core region.

In the example of FIG. 6, the temperature sensing element 512 is formedin the bulk silicon material. For example, the temperature sensingelement 512 is a diode formed by doping the corresponding portion of thebulk silicon 602 (e.g., to create a corresponding P-N junction. Theanode and cathode of the diode 512 can be coupled to respective outputterminals (not shown, but see, e.g., 118 and 128) through respectiveinterconnects. As mentioned, a current source can be coupled to theanode to bias the diode and the voltage across the diode can vary inresponse to heating of the central core region 506 (by current flowingthrough heating element 502). The insulating layer 608 is formed overthe bulk silicon base layer 602 and the corresponding portion of thecore region 506. For example, the insulating layer is an oxide layerthat may be grown or deposited (e.g., by thermal oxidation or vapordeposition) on the bulk silicon through an appropriate fabricationprocess. As an example, the insulating layer 608 is formed of aninter-metal dielectric (e.g., oxide layer) that provides galvanicisolation between the input and output of thermal converter circuit. Thethickness of the dielectric layer 608 can be increased or otherwisecontrolled to control the voltage breakdown between the heating element502 and sensing element 512 in the bulk silicon 602. The heating element502 is formed in or over the insulating layer 608, such as describedherein. For example, if a lower voltage breakdown may suffice, theresistive heating element may be formed in the silicon base layer (e.g.,a diffused resistor). It this example, the resistive heating element iselectrically separate from the temperature sensing element by junctionisolation.

As shown in FIG. 6, a passivation layer 612 is formed over theinsulating layer 608 and the heating element 502, which defines asurface (e.g., shown as a top surface) of the central core region 506.For example, the passivation layer 612 is formed of a glass (e.g., asilicate or borophosphosilicate glass film) or other insulatingmaterial, such as a nitride or silicon dioxide, which is grown ordeposited (e.g., by chemical vapor deposition) over the insulating layer608 and heater 502. As mentioned, interconnects 510 (e.g., correspondingto the interconnect 510) may be formed on the arms and extend throughvias formed in the passivation layer to couple to the heating andtemperature sensing elements. For example, a pair of interconnects canbe coupled to ends of each respective heating element and to respectiveends of each temperature sensing element.

During formation of the MEM structure 500, the substrate regionsurrounding the core region 506 is removed, such as by etching (e.g.,chemical etching, plasma etching or the like), so that the central coreregion is floating in the cavity 614. A cap layer 620 of a substratematerial (e.g., another bulk silicon wafer) is applied to enclose thefloating central core region 506 between the base layer 604 and the caplayer. For example, the cap layer 620 is applied to hermetically sealand form an enclosure around the floating central core region 506 in theMEM structure 500 and the surrounding cavity 614. That is, the supportarms 508 support the central core region 506 within the cavity 614 thatcontains a vacuum or inert gas surrounding the central core region 506.

Even though the thermal conductance of the insulating layer 608 (e.g.,an oxide layer) may be substantially less (e.g., about 10 times less)than silicon, because the core region 506 is enclosed within a vacuum orinert gas and has minimal thermal loss out of the support arms, theoxide layer affords a high dielectric voltage standoff while alsoachieving high sensor gain relative to the heated region temperaturerise versus the input signal level. That is, the thermal converterformed by the resistive heating element 502 and the temperature sensingelement 512 in the bulk silicon provides a high level of sensitivity tothe input signal. The insulating layer 608 between the heating element502 and the temperature sensing element 512 provides galvanic isolationbetween the input and the output of the thermal converter circuit.Additionally, the mass of the central core region 506 provides foraveraging or the “mean” portion of the RMS calculation that isimplemented by the thermal converter. This enables the thermal converterto achieve a desired low cutoff frequency for the thermal low passfilter. For example, the thermal converter has a transfer function thatis root-square at DC and low frequency and, as frequency increases, thethermal mass and thermal resistance of the assembly averages (e.g.,provides the mean). The thermal resistance between the heating elementand the diode and the thermal mass of the core region thus providedesign parameters that can be configured to adjust the cutoff frequencyof the thermal converter. As a result, the thermal converter can operateto a DC input level where the transfer function of the circuit is linearand rectifying. In practice, frequencies in the MHz and GHz are filteredby the thermal converter on the MEM structure and lower frequencies maybe filtered adequately in post processing.

FIG. 7 depicts an example of a sensor device 700. The sensor device 700includes a pair of MEM structures 702 and 704. Each of the MEMstructures 702 and 704 may be implemented according to any of theexamples disclosed herein (e.g., FIG. 1, 5 or 6). In the example of FIG.7, the device 700 includes a pair of MEM structures, although the sensordevice 700 may be constructed to have different numbers of MEMstructures, such as according to the examples FIGS. 3 and 4. Each of theMEM structures 702 and 704 includes a resistive heating elementdemonstrated schematically as RA and RB, respectively. Each MEMstructure 702 and 704 also includes a respective temperature sensingelement demonstrated as diodes DA and DB, respectively. The heatingelement RA and sensing element DA of MEM structure 702 are implementedon a central core region 706 of the MEM structure. The central coreregion 706 is supported by an arrangement of arms 708 connected betweenthe core and the surrounding substrate. For example, the support arms708 configured to support the central core region 706 to be floating ina cavity (e.g., containing a vacuum or an inert gas) within thesurrounding substrate. In the example of FIG. 7 the support arms extendalong each side portion of the central core region 706 in a symmetricalmanner. The support arms 708 and cavity thus cooperate to providethermal and mechanical isolation between the core region 706 and thesurrounding substrate material. The second MEM structure 704 may beconfigured as an identical or proportional replica of the MEM structure702. Briefly, the MEM structure 704 includes a corresponding centralcore region 710 that is supported by an arrangement of support arms 712.

The resistive heating element RA of MEM structure 702 is coupled toinput terminals 720 and 722, such as through corresponding interconnectsthat are coupled to ends of the resistive heating element formed in thecentral core region 706. Thus in response to applying an input signalVIN to the input terminals 720 and 722, the electric current through theheating element causes a rise in temperature that is transferred throughdielectric insulation to the bulk silicon of the central core region.The rise in temperature, however, is thermally insulated from thesurrounding substrate and circuitry through the vacuum or inert gas thatis contained in the surrounding region.

The heating of the central core region 706 induces a forward voltagedrop change in the diode DA which is coupled to an input 724 of anamplifier 726. A current source also may be coupled to bias the diode DAthrough a corresponding interconnect coupled to the anode thereof, asschematically shown. Another end of the diode DA may be coupled toelectrical ground through another interconnect. The voltage across thediode DA varies as a function of the heating of the central core region706 and thus represents an RMS value of the input signal VIN. Thevoltage across the diode is provided as an output signal to the inputterminal 724 of the amplifier 726.

In the example of FIG. 7, an output 728 of the amplifier 726 is coupledto a node (terminal 732) of the resistive heating element RB and anothernode of the heating element is coupled to electrical ground through aterminal 730. The output 728 of the amplifier 726 thus is configured todrive current through the resistive heating element RB based on thesensed temperature of the central core region 706 as provided by sensingelement DA and based on temperature detected by sensing element DB forthe central core region 710. For example, the anode of the diode DB iscoupled to the non-inverting input 734 of the amplifier 726. A currentsource is also coupled to the diode DB to bias the diode, such thevoltage across the diode DB due to heating of the central core region710 through diode represents the heating of the central core region 710.

In this closed loop configuration, the amplifier 726 provides a feedbackfor driving the resistive heating element RB. As mentioned, theelectrical characteristics of the central core region 706 and 710 can beidentical as well as the thermal characteristics of the respectiveregions. When the servo implemented by the amplifier 726 is balanced andthe temperature of the two core regions 706 and 710 are equivalent, theoutput signal V_(OUT) across terminals 730 and 732 is equal to theequivalent heating value or the RMS value of the input signal V_(IN)that is applied to terminal 720 and 722. Due to the matching and closedloop nature of the sensor device 700, the transfer function is linearand has wide bandwidth. Additionally because the area to be heated byeach of the respective resistive heating elements RA and RB isrelatively small (e.g., on the order of tens of micrometers or largerdepending on application), the sensing device has high sensitivity. As afurther example, at low frequencies or DC inputs, the output signalV_(OUT) will directly follow an absolute magnitude of the input signalV_(IN) until a corner frequency of the thermal LPF is reached. Thecorner frequency can be set based on the mass of the heated region andthe thermal conductivity to that region. Additionally, at highfrequencies (e.g., greater than the crossover frequency), the outputsignal V_(OUT) provides an RMS or mean value of the input signal VIN. Insome examples, the crossover frequency may be a design parameter thatmay be adjusted based on the size (mass) of the central core region 706,710.

FIG. 8 depicts an example of another sensor device 800 that isconfigured as a closed loop sensor similar to the sensor 700 of FIG. 7.The sensor device 800 includes MEM structures 802 and 804 that may beimplemented as described with respect MEM structures 702 and 704 of FIG.7. Accordingly, references numbers used for features in the sensordevice 800 of FIG. 8 are the same as those used to refer to the samefeatures in FIG. 7 but are increased by adding one hundred. Thus,briefly stated, the MEM structure 802 thus includes a central core 806that is supported by arms 808 and the central core region includesheating element RA and temperature sensing element DA. Similarly, a MEMregion 804 includes a central core region 810 that is supported by arms812 and terminals 830 and 832 are coupled to end nodes of resistiveheating element RB. The temperature sensing element DA is coupledbetween input 824 of the amplifier 826 and electrical ground. Similar,the input of temperature sensing element DB is coupled to another input834 of the amplifier 826 and electrical ground. Current sources 840 and842 supply current to bias diodes DA and DB, respectively. The device800 also includes inputs 820 and 822 and outputs 830 and 832.

In the example of FIG. 8, the amplifier 826 and associated currentsource circuits 840 and 842 are implemented on a central core region 850of another MEM structure 852. The MEM structure 852 also includessupport arms 854 that support the central core region 850 relative tothe surrounding substrate of the structure. In this way the circuitry826, 840 and 842 is mechanically and thermally isolated within the MEMstructure and thus are not subjected to package stress. In the exampleof FIG. 8, the output of the amplifier 826 is coupled to drive theheating element RB through a corresponding buffer 860. In this example,the buffer 860 is formed in the substrate outside of the central coreregion 850. In other examples, the buffer 860 could also be implementedin the central core region 850 or within its own central core of anotherMEM structure (not shown) or in a circuit external to the device 800.

The examples of FIGS. 7 and 8 demonstrate that the various circuitryutilized to implement a sensing device, as disclosed herein, may beintegrated within one or more MEM structures or, alternatively, certaincircuitry (e.g., thermal converter circuitry) may be implemented in MEMstructures while other circuitry may be external to any MEM structuresand be coupled to the MEM structures through corresponding interconnectswithin a given sensor package. For example, components and circuitry(e.g., thermal converter circuitry) that may be stress-sensitive can beisolated in their own central core region of respective MEM structureswhile other circuitry resides external to such MEM structure(s).

FIG. 9 depicts an example of another sensor device 900. The sensordevice 900 is implemented in an open loop configuration and configuredto provide an ERROR signal based on input signals VIN1 and VIN2. Thesensor device 900 includes input terminals 902 and 904 to receive theinput signal VIN1 and another set of input terminals 906 and 908 adaptedto receive the signal VIN2. The input signals can be from one or moreassociated circuit for which the sensing and generating of the ERRORsignal is desired. The sensor device 900 also includes a pair of MEMstructures 910 and 912, such as may be implemented as any MEM structuresdisclosed herein (e.g., 102, 104, 202, 204 500).

The sensor device 900 is configured to provide the ERROR signal based ona difference in the RMS value of the respective input signals VIN1 andVIN2. For example, the MEM structure 910 includes a thermal converterformed by a resistive heating element RA that is coupled between inputterminals 902 and 904. The temperature sensing element DA is coupledbetween an input 918 of an amplifier 920 and electrical ground. Acurrent source 922 is coupled to bias the diode DA, such that changes intemperature are reflected in the voltage across the diode DA at theinput 918. The MEM structure 910 may be configured according to any ofthe examples disclosed herein, and thus includes a supporting structure,such as support arms 924 configured to support a perimeter portion of acentral core region 926 within a cavity that may include a vacuum orinert gas. In this way, the signal provided at the input 918 of theamplifier 920 represents an RMS value of the input signal VIN1.Similarly, the MEM structure 912 includes a support arms 928 configuredto support a perimeter portion of a central core region 930 within acavity that contains a vacuum or inert gas. The output of thetemperature sensing element DB thus provides a corresponding RMS valueof the input VIN2 at the input 934 of amplifier 920. In this way, theamplifier 920 produces the ERROR signal to indicate a difference in theRMS values of the different inputs VIN1 and VIN2. The error signal maybe used in other systems such as for balancing signals VIN1 and VIN2,fault detection or the like.

FIG. 10 depicts an example of a sensor circuit package 1000. The package1000 includes a sensor device that includes two or more MEM structures1002, such as according to any of the examples disclosed herein (e.g.,FIGS. 1, 2, 5 and 6). Each MEM structure 1002 may be implemented on arespective die or a multiple MEM structures may be implemented on agiven die. For example, each such MEM structure 1002 includes a centralcore region 1004 that includes a thermal converter circuit formed of aheating element and a sensing element, such as disclosed herein. Thecentral core region 1004 thus may be implemented as a multi-layerstructure in which the heating element is spaced from the sensingelement by one or more insulating layers. The central core region 1004is supported within the MEM structure to be floating, such as beingsurrounded by a cavity that includes a vacuum or contains an inert gas.Thus, the central core region 1004 is thermally and mechanicallyisolated from the surrounding substrate material.

As shown in the example of FIG. 10, a cap layer 1006 is disposed over alayer to enclose and hermetically seal the MEM structure 1004 betweenthe cap layer 1006 and a bulk substrate base layer 1008. As disclosedherein, the central core region 1004 is supported in the cavity withrespect to the surrounding substrate through a support structure, suchas a symmetrical arrangement of support arms coupled between thesurrounding substrate and a given insulating layer of the central core.

The circuitry implemented within the central core region 1004 may becoupled to the surrounding substrate through an arrangement ofinterconnects (e.g., interconnects 510). Each of the respectiveinterconnects thus may extend through one or more layers and couple toappropriate ends of the circuit components, such as disclosed herein(see, e.g., FIG. 5). In the example of FIG. 10, the MEM structure 1002is encapsulated within a packaging material 1010, such as plastic (e.g.,a thermosetting polymer or thermoplastic material) or an epoxy moldingmaterial. The substrate base layer 1008 is also disposed or attached toa corresponding lead frame 1012. A number of leads 1014 may be coupledbetween the MEM structure 1004 and the lead frame 1012. The leads thusprovide electrical connections between the circuit componentsimplemented on the central core region 1004 and input terminals (e.g.,pins, pads or the like) that may be accessed by a circuitry external tothe package 1000.

Because each of the MEM structures 1002 is sealed in a hermeticenclosure and floating with respect to the surrounding substratematerial, the circuitry implemented on the central core region isafforded isolation from mechanical package stress and temperaturevariations. Additionally, the die or a number of die can be packaged ina respective single or multi-chip module that can be packaged accordingto standard, low-cost injection molded plastic packaging technologies.This enables the circuitry implemented on the central core region 1004to maintain thermal isolation and accurate circuit performance that isindependent of mechanical stress in the plastic packaging, customerprinted circuit board to which the package is mounted, and other inducedenvironmental conditions (e.g., humidity variations).

By way of further example, FIGS. 11-16 illustrate examples of differentcircuits that may be configured to implement sensor devices utilizingtwo or more MEM structures as disclosed herein. That is, each of theexamples of FIGS. 11-16 includes a sensor device package 1102 thatincludes two or more MEM structures (e.g., single or multi-chip modules)1104 and 1105 having sensor circuitry coupled to external circuitry toimplement various sensing circuits. The sensor circuit package 1102includes input terminals 1106 and 1108 coupled to receive an inputsignal VIN and electrical ground, respectively. In these examples, thesensor circuit package 1102 also includes output terminals 1110 and1112; however, in other examples (e.g., an open loop sensorconfiguration—see, e.g., FIG. 17), the terminals 1110 and 1112 could beinput terminals. For example, the sensor circuit package 1102 may beimplemented according to the examples of FIG. 7 or 8 and thus includetwo or MEM structures (e.g., structure 500 of FIGS. 5 and 6) 1104 and1105. As disclosed herein, the MEM structures 1104 and 1105 areconfigured to implement a thermal converter that provides an outputsignal at 1110 representing a true RMS value of the input signal VIN.While the external circuitry in the examples of FIGS. 11-16 aredemonstrated as external to the package, in other examples, suchcircuitry also may be implemented within the package, in part or wholly.For example, such external circuitry may be implemented on acorresponding central core region of a MEM structure (e.g., similar toMEM structure 852 that includes amplifier circuitry in FIG. 8) orexternal to MEM structures. In each of the examples of FIGS. 11-16, theoutput terminal 1110 is galvanically isolated from the terminals 1106and 1108. For purposes of consistency, in the following descriptions ofFIGS. 11-16, identical reference characters are used to refer the sensorpackage 1102 and its components. Accordingly, reference may be made tothe above description and other examples disclosed herein forinformation about the sensor package 1102.

FIG. 11 depicts an example of a true RMS converter circuit 1100. Thecircuit 1100 includes the sensor circuit package 1102, as disclosedherein, that is coupled to an analog-to-digital converter (ADC) 1114.The output terminals 1110 and 1112 of the sensor package 1102 arecoupled to an input of the ADC 1114 and ground, respectively. The ADCthus is configured to convert the analog DC signal provided at 1110 to acorresponding digital representation of the RMS value.

FIG. 12 depicts an example of a low-side sensor circuit 1200. In theexample of FIG. 12, a load 1202 is coupled between a voltage rail V+ anda switch device (e.g., a metal oxide semiconductor field effecttransistor (MOSFET)) 1204. In this example, a current sense resistor1206 is connected in series with the switch device 1204 and betweenterminals 1106 and 1108 in parallel to the heating resistor of the MEMstructure 1104. For high current measurement applications, the value ofthe resistor 1206 may be several orders of magnitude lower than theheating resistor. An output of the switch device 1204 is coupled toinput terminal 1106 and terminal 1108 is coupled to ground. The outputterminal 1110 thus provides an output signal representing a true RMS DCvalue of the voltage across the current sense resistor 1206, whichvaries in response to activation of the switch device 1204. The abilityto respond to the small voltage drop across this current sense resistor1206 is enabled by the high sensitivity of the MEM structure 1104 and1105 resulting from its small size and thermally insulated construction.

FIG. 13 depicts an example of a high-side sensor circuit 1300. In theexample of FIG. 13, a voltage rail V+ is coupled to apply a respectivevoltage at terminal 1106. A switch device (e.g., MOSFET) 1304 is coupledin series with a grounded load 1302 to terminal 1108. In an example, acurrent sense resistor 1306 is connected in series with the switchdevice 1304 and between terminals 1106 and 1108 in parallel to theheating resistor of the MEM structure 1104. For high current measurementapplications, the magnitude of the resistor 1306 may be several ordersof magnitude lower than the heating resistor. In response to activationof the switch device 1304, current is applied to supply power to theload 1302. The output terminal 1110 thus provides an output signalrepresenting a true RMS DC value of voltage across the resistor 1306,which varies in response to activation of the switch device 1304.

FIG. 14 depicts an example of another sensor circuit 1400, such as forsensing current applied to a load 1402. In the example of FIG. 14, theload is coupled to terminal 1106 of the sensor device package 1102. Thesensor device package 1102 is configured to sense the current in theload as represented as a voltage drop across current sense resistor1408. A high-side switch device 1404 and a low-side switch device 1406are connected between a voltage rail V+ and electrical ground. Anintermediate node between the switch devices is coupled to the terminal1108. In an example, a current sense resistor 1408 is connected betweenterminals 1106 and 1108 in parallel to the heating resistor of the MEMstructure 1104. For high current measurement applications, the magnitudeof the resistor 1408 may be several orders of magnitude lower than theheating resistor. In this way, the voltage applied to the load 1402through the resistor 1408, such as a pulse width modulated signal 1410,is also provided to the heating element of MEM structure 1104, such thata corresponding RMS value of the voltage across the resistor 1408 isprovided at the terminal 1110.

FIG. 15 depicts an example of a DC-DC converter 1500 that includes asensor device 1102 coupled in feedback path of the converter. Forexample, the converter 1500 includes primary circuits 1502 coupled tosecondary circuits 1504 through a transformer 1506. The sensor device1102 is coupled between an output 1508 of the converter and a feedbackinput 1510 of the converter. In the example of FIG. 15 the output 1508of the converter 1500 is coupled to terminal 1106 and terminal 1108 iscoupled to ground. The sensor device 1502 is configured to sense avoltage applied to a load 1512 by the converter 1500 and provide an RMSDC signal as feedback to the input 1510 representing the load voltage.The sensor device 1102 disclosed herein may be used for providing an RMSvalue of a feedback voltage for other types of converters.

FIG. 16 depicts an example of an isolated operational amplifier 1600that includes a sensor device 1102. In the example of FIG. 16, thesensor device in which the resistive heating element of MEM structure1104 has a resistance R and the heating element of MEM structure 1105has an aggregate resistance of nR, where n is multiplier (fractional orinteger) that sets a gain of the amplifier 1600. For example, the gainmay be set (e.g., as a design parameter) by configuring an arrangementof the MEM structures 1105 in series or parallel to increase ordecrease, respectively, the gain of the amplifier 1600 accordingly. Aninput voltage (e.g., ranging from a DC input to an RF input signal) isapplied to terminal 1106. The operational amplifier 1600 provides anoutput signal VOUT at terminal 1110. For example, the output voltage at1110 may be represented as VOUT=|VIN*n|. The operation amplifier 1600 ofFIG. 16 may be used in any of the examples of FIGS. 11-15 to adjust thesensitivity of sensing based on a proportionality of the resistancevalue of respective heating elements.

FIG. 17 depicts an example of a load sensing system 1700 that includes asensor device 1702 in an open loop configuration (e.g., corresponding tosensor device 900 of FIG. 9). The open loop configuration of the sensordevice 1702 may be used for ground fault detection, load balancing orother application. For example, the sensor device 1702 that includes twoor more MEM structures 1704 and 1706, each having respective inputterminals 1708-1710 am 1712-1714. In an example, a current senseresistor 1718 is connected between terminals 1708 and 1710 and anothersense resistor 1720 is connected between terminals 1712 and 1714. Forthe example of high current measurement applications, the magnitude ofthe resistors 1718 and 1720 are several orders of magnitude lower thanthe heating resistor of respective MEM structures 1704 and 1706. Thevoltage across the resistor 1718 between terminals 1708-1710 isrepresentative of input load current ILOAD applied to a load 1716, whichis coupled between terminals 1710 and 1714. The voltage across theresistor 1720 between terminals 1712-1714 is representative of an outputload current ILOAD from the load 1716. The sensor device 1702 includescircuitry (e.g., including an amplifier 1722) that is configured toprovide an output signal at an output 1724 thereof representing adifference in the RMS value of the voltage signals applied to respectivesets of input terminals 1708-1710 and 1712-1714.

What have been described above are examples of the disclosure. It is, ofcourse, not possible to describe every conceivable combination ofcomponents or method for purposes of describing the disclosure, but oneof ordinary skill in the art will recognize that many furthercombinations and permutations of the disclosure are possible.Accordingly, the disclosure is intended to embrace all such alterations,modifications, and variations that fall within the scope of thisapplication, including the appended claims.

What is claimed is:
 1. A sensor device comprising: a firstMicro-Electro-Mechanical (MEM) structure comprising: a first heatingelement on a first layer of the first MEM structure, the first heatingelement including an input adapted to receive an input signal; and afirst temperature sensing element on a second layer of the first MEMstructure, the first layer being separated from the second layer by atleast one insulating layer; a second MEM structure comprising: a secondheating element on a first layer of the second MEM structure; and asecond temperature sensing element on a second layer of the second MEMstructure, the first layer of the second MEM structure being separatedfrom the second layer of the second MEM structure by at least oneinsulating layer; and an output circuit having a first input coupled tothe first temperature sensing element and a second input coupled to thesecond temperature sensing element.
 2. The sensor device of claim 1,further comprising a package of an electrically insulating material thatencapsulates at least the first MEM structure and the second MEMstructure.
 3. The sensor device of claim 2, wherein the output circuitincludes an amplifier having an output coupled to the second heatingelement, the amplifier being configured to drive the second heatingelement to match heating of the first heating element based on atemperature sensed by the first temperature sensing element and atemperature sensed by the second temperature sensing element such thatan output signal across the second heating element represents a rootmean square value of the input signal.
 4. The sensor device of claim 2,wherein the package also contains [OR encapsulates] the output circuit.5. The sensor device of claim 4, further comprising a third MEMstructure that is thermally and mechanically isolated from each of thefirst and second MEM structures, the third MEM structure including theoutput circuit.
 6. The sensor device of claim 2, further comprising: afirst set of support arms configured to mechanically and thermallyisolate a central core of the first MEM structure from surroundingsilicon in the package, the central core of the second MEM structurebeing spaced from the surrounding silicon by a first cavity containing avacuum or inert gas; and a second set of support arms configured tomechanically and thermally isolate a central core of the second MEMstructure from surrounding silicon in the package, the central core ofthe second MEM structure being spaced from the surrounding silicon by asecond cavity containing a vacuum or inert gas.
 7. The sensor device ofclaim 6, further comprising a base layer of a semiconductor material,the first MEM structure and the second MEM structure being spaced apartand insulated from the base layer, and a cap layer disposed over thecentral core of the first MEM structure and the central core of thesecond MEM structure to hermetically seal each of the respective centralcores and respective regions containing the vacuum or inert gas withinan enclosure between the base layer and the cap layer.
 8. The sensordevice of claim 6, wherein the central core of the first MEM structurefurther comprises: a bulk layer that includes the first temperaturesensing element; wherein the first layer of the first MEM structurecomprises a layer of an oxide material between the bulk layer and thefirst heating element to provide galvanic isolation between the firstheating element and the bulk layer; and a passivation layer disposedover the first heating element.
 9. The sensor device of claim 1, whereinthe first heating element is a resistive heating element and the secondheating element is a resistive heating element.
 10. The sensor device ofclaim 9, wherein each resistive heating element comprises one of a thinfilm resistor, a metal resistor that is disposed on an oxide layer. 11.The sensor device of claim 1, wherein the first temperature sensingelement comprises a first diode and the second temperature sensingelement comprises a second diode.
 12. The sensor device of claim 1,wherein the first temperature sensing element and the second temperaturesensing element each comprises one of a thermistor, bipolar transistor,metal oxide semiconductor field effect transistor or thermocouple. 13.The sensor device of claim 1, wherein: the input of the first heatingelement is a first input of the sensor device and the input signal is afirst input signal, the second heating element includes a second inputof the sensor device adapted to receive a second input signal, and theamplifier is configured to provide an output signal at an output thereofrepresenting a difference in root mean square values of the first inputsignal and the second input signal.
 14. The sensor device of claim 1,wherein the first MEM structure and the second MEM structures arematched replicas of each other.
 15. A sensor circuit package comprising:at least two Micro-Electro-Mechanical (MEM) structures, each of the MEMstructures comprising: a central core region including a thermalconverter circuit that is configured to heat the central core region inresponse to a signal at an input thereof and to provide an temperaturesignal representing a temperature of a heated area of the central coreregion; and a support structure coupled between the central core regionand surrounding substrate, the support structure configured to supportthe central core region to be thermally and mechanically isolated withrespect to the surrounding substrate; and an amplifier circuitconfigured to provide an amplifier signal at an output of the amplifierbased on the output signals provided by the thermal converters of therespective MEM structures.
 16. The sensor circuit package of claim 15,wherein: the at least two MEM structures comprise first and second MEMstructures, the input of the thermal converter circuit of the first MEMstructure is coupled to an input terminal of the package, and the outputof the amplifier circuit is coupled to a heating element of the thermalconverter circuit of the second MEM structure and to an output terminalof the package, wherein the output terminal is galvanically isolatedfrom the input terminal.
 17. The sensor circuit package of claim 16,wherein the amplifier is configured to drive current to the heatingelement of the thermal converter circuit of the second MEM structurebased on a temperature sensed by a first temperature sensing element ofthe first MEM structure and a temperature sensed by a second temperaturesensing element of the second MEM structure such that an output signalat the output terminal represents a root mean square value of an inputsignal applied at the input terminal.
 18. The sensor circuit package ofclaim 17, wherein the first temperature sensing element and the secondtemperature sensing element each comprises one of a diode, thermistor,bipolar transistor, metal oxide semiconductor field effect transistor orthermocouple.
 19. The sensor circuit package of claim 15, wherein: theat least two MEM structures comprise first and second MEM structures,the input of the thermal converter circuit of the first MEM structure iscoupled to a first input terminal of the package, the input of thethermal converter circuit of the second MEM structure is coupled to asecond input terminal of the package, the first input terminal beingisolated from the second input terminal, and the amplifier is configuredto provide an output signal at the output of the amplifier representinga difference in the root mean square value of signals applied at thefirst and second input terminals.
 20. The sensor circuit package ofclaim 15, wherein the central core region of the each of the MEMstructures is supported within a cavity by support arms, and the centralcore region of the each of the MEM structures further comprises: asubstrate layer that includes a temperature sensing element coupled toan input of the amplifier; an insulating layer over the substrate layer;a heating element over the insulating layer, the insulating layerconfigured to provide to provide galvanic isolation between the heatingelement and the temperature sensing element; and a passivation layerdisposed over the heating element.
 21. The sensor circuit package ofclaim 20, wherein each of the MEM structures further comprises: a caplayer disposed over the central core region to hermetically seal thecentral core regions and the cavity surrounding the respective centralcore regions within an enclosure between a base layer and the cap layer.22. The sensor circuit package of claim 15, further comprising a leadframe, the lead frame comprising terminals coupled to the output of theamplifier and the input of at least one thermal converter.